1. Technical Field
The present invention relates to a substrate cleaning tool, apparatus, and method that are used in the cleaning of a substrate such as a semiconductor wafer.
2. Description of Related Art
During the fabrication of a semiconductor device, it is necessary to ensure a high level of cleanliness of the surfaces of the semiconductor wafer (hereinafter called xe2x80x9cwaferxe2x80x9d) on which the semiconductor device is to be formed. For that reason, a substrate cleaning apparatus is used to clean the surfaces of the wafer at various stages, such as before and after each fabrication step or processing step, or after film-formation steps and polishing steps.
A substrate cleaning apparatus of this type has been disclosed in Japanese Patent No. 2875213, by way of example. This apparatus presses a head against the surface of the wafer, while the wafer is made to rotate, and removes particulate contaminants from the surface of the wafer by the relative motion between the wafer and the head.
In the substrate cleaning apparatus of this Japanese Patent No. 2875213, the head is configured of a protective film covering the surface of a cell-structure of foamed polyvinyl alcohol (PVA). Various other types of head are used in known substrate cleaning apparatuses, such as a stiff head formed of a material such as a head with hard and stiff nylon bristles or a flexible head formed of a material such as soft mohair, by way of example, and these heads have to be used differently as appropriate, depending on the type of cleaning.
With the substrate cleaning apparatus disclosed in Japanese Patent No. 2875213, particles of contaminants or the like readily adhere to the protective film, these particles are transferred to the wafer, and there is a fear that the particles will remain on the wafer after the cleaning. With a head such as a nylon head or mohair head, there is also the fear of damage to the surface of the wafer from friction or scratching, particularly with a stiff head, in addition to contamination of the wafer due to the transfer of particles. With such a prior-art head, the surface of the head becomes worn as the number of cleaning cycles increases, which leads to bias or xe2x80x9cquirks,xe2x80x9d making it difficult to maintain the initial contact pressure and thus causing defective cleaning.
An object of the present invention is to provide a substrate cleaning tool that can maintain the initial contact pressure and clean a substrate in a satisfactory manner, with little adhesion of particles, no damage due to friction or scratching, and without creating bias or xe2x80x9cquirksxe2x80x9d due to wear of the surface thereof, together with a substrate cleaning apparatus and substrate cleaning method using that substrate cleaning tool.
In order to solve the above described problem, one aspect of the present invention relates to a cleaning tool for cleaning a substrate, the cleaning tool including: a cleaning head and a cleaning liquid supply path for supplying a cleaning liquid into the cleaning head; wherein the cleaning head comprises: a permeable core member and a permeable porous film covering an outer surface of the core member.
Cleaning is done with this cleaning tool by pressing the cleaning tool onto the surface of the substrate while a cleaning liquid is supplied through the cleaning liquid supply path, then causing the substrate and the cleaning tool to move relative to each other. The cleaning liquid supplied through the cleaning liquid supply path passes through the core member and the tiny holes formed in the porous film and is expelled onto the substrate, in a state in which the cleaning liquid is constantly expelled onto the surface of the substrate. There is therefore no need to worry about particles adhering to the surface of the substrate (in other words, to the surface of the porous film). This means that there is no need to worry about particles entering into the porous film, and there is no problem concerning contamination of the substrate by the transfer to the substrate of particles that have adhered to the porous film.
Moreover, since the porous film is placed into contact with the substrate in a state in which a liquid film is formed on the surface of the substrate by the expelled cleaning liquid, the contact between the porous film and the substrate can be done smoothly. In particular, if the porous film is placed indirectly into contact with the substrate, with the liquid film formed on the surface of the substrate therebetween, the contact between the porous film and the substrate can be done smoothly. This ensures that there is no damage to the substrate. In addition, since the porous film covers the core member, there is no need to worry about deformation of the porous film due to the supply pressure of the cleaning liquid, which makes it possible for the porous film to maintain its predetermined shape always. Since the contact between the porous film and the substrate is smoothed, there is no destruction of the shape thereof due to friction or other factors, even when the number of cleaning cycles increases.
The cleaning head may comprise a surface facing a substrate, that surface is formed to be a planar surface, and that planar surface is covered by the porous film. The cleaning head is preferably configured to comprise a cylindrical portion, wherein the planar surface is formed at an end portion of the cylindrical portion.
The permeable porous film is typically formed of a synthetic resin. The synthetic resin of the porous film may be either a hydrophilic resin or a hydrophobic resin.
The planar surface may have a groove through which a flow of the cleaning liquid is produced.
Another aspect of the present invention provides an apparatus for cleaning a substrate. This substrate cleaning apparatus comprises: a cleaning tool and a support mechanism for supporting the cleaning tool, a pressing mechanism for pressing the cleaning tool to the substrate; wherein the cleaning tool comprises a cleaning head and a cleaning liquid supply path for supplying a cleaning liquid into the cleaning head; and the cleaning head comprises: a permeable core member for receiving the supply of cleaning liquid from the cleaning liquid supply path and a permeable porous film covering an outer surface of the core member.
The pressing mechanism may be a pneumatic device. The cleaning liquid supply path may be provided with an ultrasonic wave generator for imparting ultrasonic wave oscillations to a cleaning liquid that passes therethrough.
A further aspect of this invention relates to method of cleaning a substrate, comprising the steps of: expelling a cleaning liquid from a cleaning tool formed of a permeable core member covered with a porous film, which is supplied with a cleaning liquid from a cleaning liquid supply path; and cleaning a surface of the substrate in a state in which a liquid film is formed between the surface of the substrate and the cleaning tool by the cleaning liquid expelled from the cleaning tool.
A still further aspect of this invention relates to a substrate cleaning method comprising the step of expelling a cleaning liquid through a cleaning tool that is formed of a permeable core member covered with a porous film, which is supplied with a cleaning liquid through a cleaning liquid supply path, and the step of cleaning a substate with the cleaning tool; wherein the cleaning method further comprises the steps of: recording a signal value into a control portion, for obtaining a predetermined contact pressure of the cleaning tool with respect to the substrate, before the substrate is cleaned by the cleaning tool; performing the cleaning while pressing the cleaning tool against the substrate; and controlling the pressing force of the cleaning tool so as to obtain the predetermined contact pressure.